1. Field of the Invention
The disclosures herein generally relate to a surface-emitting laser apparatus and a manufacturing method thereof.
2. Description of the Related Art
Recently, intensive investigations have started on high-power lasers, for such as various kinds of optical instruments, laser projectors or light source lasers for laser processing machines. Such high-power lasers have achieved high output by focusing light from surface-emitting laser arrays, for example. A surface-emitting laser is suitable for a light source of a high-power laser according to a characteristic that light is emitted in a direction orthogonal to a substrate, a characteristic of easy integration and a characteristic of being easily testable. As a configuration of the high-power laser, for example, a configuration has been known in which a collimator lens including a microlens array is arranged in a light emission direction of a surface-emitting laser array which is a light source and furthermore a light focusing lens is arranged.
A surface-emitting laser array has a configuration, in which surface-emitting lasers each having a mesa structure several tens of micrometers square as a unit element are arranged in a square lattice shape or in a hexagonal closed packed lattice shape. On the other hand, a microlens array for generating collimator light from the light emitted from the surface-emitting laser array is made of synthetic quartz or the like and is formed corresponding to the unit element of the surface-emitting laser array.
The configurations of the surface-emitting laser array and the microlens array, as described above, requires high mounting accuracy of ±tens of micrometers in three directions of X, Y and Z for mounting the microlens on the surface-emitting laser in order to improve utilization efficiency of light of the surface-emitting laser. Then, various investigations for improving accuracy of mounting a microlens on a surface-emitting laser have been performed. Specific examples in the related art of aligning a microlens with a surface-emitting laser with high accuracy are as follows:
The first example in the related art of aligning a microlens with a surface-emitting laser is a photonic device. The photonic device is a device in which the surface-emitting laser and the microlens are integrated. The photonic device has a microlens structure, in which plural leg portions are provided on a substrate on which the surface-emitting laser is formed in order to keep a predetermined distance from the surface-emitting laser.
In the photonic device, as described above, mounting with high accuracy in the Z-direction is possible by fixing the leg portions, which are integrated with the microlens structure and are extended, on a surface of the substrate on which the surface-emitting laser is formed. Meanwhile, for aligning in the XY-directions, two kinds of positioning methods, i.e. positioning while monitoring images of the surface-emitting laser and of the lens and positioning while causing the surface-emitting laser to emit light and receiving light having transmitted through the lens, are disclosed (See, for example, Japanese Published Patent Application No. 2007-142425).
The second example in the related art of aligning a microlens with a surface-emitting laser is an optical element mounting apparatus. In the optical element mounting apparatus, in order to make it possible to align with high accuracy in the X, Y and Z directions, a protrusion of an alignment reference portion is integrally formed on one side of a microlens array substrate. Then, a depression of the alignment reference portion is integrally formed on one side of a surface-emitting laser array substrate. By engaging both the alignment reference portions, the mounting with high accuracy is possible.
Meanwhile, in the above-described optical element mounting apparatus, the protrusion on the side of the microlens is formed integrally with the microlens upon resin molding of the microlens, and the depression on the substrate on the side of the surface-emitting laser array is manufactured with high accuracy by etching using a photolithography technology of a semiconductor process. According to the above, mounting accuracy after assembly is guaranteed (See, for example, Japanese Published Patent Application No. 2004-288713).
The third example in the related art of aligning a microlens with a surface-emitting laser is a surface-emitting type light source. In the surface-emitting type light source, a microlens is formed corresponding to each surface-emitting laser, which is a unit element, on a surface-emitting laser array substrate. Meanwhile, by molding dielectric material such as SiO2 film formed on a surface of the surface-emitting laser into a microlens by photolithography technology, the microlens makes it possible to align the surface-emitting laser and the microlens with high accuracy during manufacture (See, for example, Japanese Published Patent Application No. 2002-26452).
However, the first example of the related art has a problem that, in order to implement the above-described two kinds of positioning methods, a complicated and expensive mounting apparatus is required and a mounting takt is slow. That is, it is difficult to align a microlens on a surface-emitting laser with high accuracy by a simple method.
Moreover, in the second example of the related art, since a height of the protrusion and a depth of the depression are less than or equal to a thickness of the substrate at most, the height of the protrusion and the depth of the depression are less than or equal to several hundreds of micrometers. That is, the height of the protrusion is quite low, and the depth of the depression is quite shallow. There is a problem that they are easily misaligned. Accordingly, the microlens is required to be fixed on the surface-emitting laser by using adhesive agent, brazing material or the like. There is a problem that misalignment of the lens may occur in the process. That is, it is difficult to align a microlens with a surface-emitting laser with high accuracy by this method.
Moreover, the third example of the related art has a lot of technical problems for implementing. Since a microlens is formed of dielectric material or the like directly on a surface-emitting laser array substrate, reliability of the surface-emitting laser may be degraded according to a stress from the dielectric material in the microlens substrate or the like. That is, practical realization of aligning a microlens with a surface-emitting laser with high accuracy by this method is difficult.
The present invention has been made in view of the above, and has an object to provide a surface-emitting laser apparatus or the like in which a microlens is aligned with a surface-emitting laser with high accuracy by a simple method.